Electrical contactors are utilised to provide a load-disconnect function in modern electricity meters, for applications such as split-phase domestic supply. A basic meter, which has an internally-mounted electrical contactor, is pluggable into a cabled utility-owned meter-base socket for ease of installation and removal. The cables and sprung jaws thereof are typically sized for delivering a 200 Amps current supply.
At the nominal 200 Amps level, the meter contactor is expected to be capable of performing a minimum number of on/off switching-cycle operations, typically 5000 of each, throughout their endurance life. This must be successfully performed without the contacts burning or welding together, when driven by the main meter circuit, for the desired on/off disconnect sequence.
According to the ANSI C12.1 specification, for a two-pole contactor, during a moderate short-circuit fault, whilst current-carrying and in the contacts-closed condition, of 5.0 kA rms, for a maximum duration of 6 full supply cycles, the contacts must not weld, and the contactor is expected to operate and disconnect both phases of the load normally, on following solenoid-driven pulses.
Similarly, according to the ANSI C12.1 specification, during a dead short fault, whilst current-carrying and in the contacts-closed condition, of 12 kA rms, for a maximum duration of 4 full supply cycles, the contacts must weld safely. This means that both of the phase switches must remain closed, must not explode, rupture or emit dangerous molten metal, and must remain intact within the meter, with no danger to nearby persons.